First detection of the amphibian chytrid fungus Batrachochytrium dendrobatidis in free-ranging populations of amphibians on mainland Asia: survey in South Korea.

Chytridiomycosis, a disease that has caused amphibian population declines globally and elevated many species of anurans to endangered or threatened status, has recently been declared an internationally notifiable disease. Batrachochytrium dendrobatidis (Bd), the amphibian chytrid fungus causing this disease, has not been previously reported in Korea or on mainland Asia. Thirty-six frog specimens representing 7 species were collected from the wild in South Korea and examined for Bd using standard PCR. Bd was detected in 14 (38.8%) samples from 3 species (Bufo gargarizans, Hyla japonica, and Rana catesbiana). Skin sections from all 14 PCR-positive frogs were examined using 2 staining techniques: haematoxylin and eosin (H&E) and Bd immunoperoxidase (IPX). In histological sections, zoosporangia were found in 6 frogs, with lower sensitivity for H&E (21%) than for IPX (46%). Intensity of infection, based on histopathology, was low in all frogs. These results confirm that Bd is present in South Korea and, hence, on the Asian mainland. Studies are urgently required to determine the impact of chytridiomycosis on Korean amphibians, and to map the distribution of Bd in Korea and other Asian mainland countries.